Calmodulin plays multiple roles in the regulation of skeletal muscle phosphorylase kinase. Calmodulin is a non-dissociable subunit of phosphorylase kinase and added calmodulin is also an activator of non-phorphorylated phosphorylase kinase. Studies in this laboratory have shown that calmodulin inhibits the activation of skeletal muscle phosphorylase kinase by protein kinase. Protein kinase activates phosphorylase kinase by the esterification of phosphate from ATP onto serine residues of the Beta and perhaps the Alpha subunits. The calmodulin inhibition has been shown to be specific for the Beta subunit. The aims of this proposal are to: 1) to determine the mechanism of the inhibition by calmodulin of the protein kinase phosphorylation of phosphorylase kinase by measurements of the kinetic and thermodynamic parameters of the inhibition; 2) to extend the study of the specificity of inhibition at the Beta subunit and relate that observation to the preliminary evidence that the active inhibitor is a calmoduline-phosphorylase kinase complex; 3) to determine whether calmodulin can inhibit the phosphorylation of cardiac phosphorylase kinase using the beef heart enzyme; 4) to determine the relationship between calcium ion concentration and the activating and inhibiting roles of calmodulin using calcium buffers; 5) to determine whether the calmodulin-phosphorylase kinase complex can inhibit phosphorylatiom by protein kinase of other substrates such as glycogen synthase; 6) to determine whether the other calcium binding proteins, parvalbumin and troponic C also act as inhibitors. The analysis of the relationship between calmodulin, phosphorylase kinase and calcium ion concentration will provide a better understanding of the control of glycogen matabolism in skeletal and cardiac muscle.